Charging vehicle batteries in cold weather

One of the biggest misconceptions in the heavy duty trucking industry is that batteries charge the same throughout the year, say officials at Purkeys Fleet Electric, a company that has been serving heavy duty fleets’ electrical needs for over 20 years. “They simply don’t.”

In warm weather (above 40F), batteries are very easy to recharge, they say. Batteries can normally take as much charge as the vehicle charging system can provide.

Even deeply discharged battery packs can be completely recharged in a few hours if the only issue is a discharged battery, not defective batteries, note the officials.

“However, the colder it is outside, the less charge the battery pack wants to accept. When it is very cold, the electrolyte in a flooded cell battery becomes like jelly and the molecular action in the battery slows down.”

The battery is similar to a tube of toothpaste - difficult to get out and almost impossible to put back in, according to the officials.

The truck operator may become fooled by the way the vehicle responds in cold weather, they say. The voltmeter on the dash displays a correct charging range and the lights are bright, so it is assumed that the batteries are charging as normal.

What is really happening is that the vehicle’s alternator is at the correct voltage and is powering the vehicle loads, they explain. But because the batteries are cold, the charge acceptance of the batteries is very low, sometimes as low as 2 amps per hour.

“Driving times of up to 40 hours can be required to charge deeply discharged cold batteries.

“While AGM batteries have up to 40 percent better recharge capacity across all temperature ranges, they will still require more time in cold weather to recharge than driving laws allow.”

- Cold batteries will not accept a normal charge until the batteries reach an ideal temperature or extensive charging time is available.

- Cold batteries can take up to 30 hours to warm back up to room temperature.

- While jump-starts can get the vehicle started, many hours of charging may be required to recharge the battery pack. It might be a more prudent path to change batteries as normal vehicle operation cannot recharge the battery pack adequately during a normal workday.